Process for producing a graphite anode



OC- 3 1967 HlRosHl sHlBATA ETAL 3,345,283

PROCESS FOR PRODUCING A GRAPHITE ANODE Filed June 5, 1963 2 Sheets-Sheet l F/E. /6 y INVENTORS OCL 3, 1967 HxRosHl SHIBATA ETAL 3,345,283

PROCESS FOR PRODUCING A GRAPHITE ANODE v Filed June 5, 1965 2 sheets-sheet 2 JNVENToRs manifs United States Patent O 3,345,283 PROCESS FR PRODUCING A GRAPHITE ANODE Hiroshi Shibata, Yasuo Yamasaki, and Kinzo Sugihara, Nakoso, Fukushima Prefecture, Japan, assignors to Kureha Chemical Industry Co., Ltd., Tokyo, Japan, a corporation of Japan Filed'luue 5, 1963, Ser. No. 285,771 Claims priority, application Japan, July 5, 1962, 37/28,209, 37/37,061 3 Claims. V(Cl. 204294) ABSTRACT OF THE DISCLOSURE A graphite anode for the electrolysis of alkaline salt solutions in an electrolytic cell having a mercury electrode is produced by impregnating the graphite electrode and coating the conductive connector pole composed of a metal having a lower electrical resistance than graphite, with a chlorine resistant material.

The present invention relates to a process for producing a graphite anode for an electrolytic cell used in the electrolysis of alkaline salt solutions by the mercury process.

An object of this invention is to produce a process for making an anode operable at a high current density.

Another object of this invention is to obtain anodes of low electrolyzing voltage at a high current density.

A further object of this invention is to produce durable anodes, wherein the amount of graphite'consumption is less at a high current density.

Still another object of the present invention is to heighten the original unit of graphite. Y

A still further object of this invention is to increase the long-term lcontinuous operation of an electrolytic cell by prolonging the interval for cleaning the electrolytic cell. Y With regard to the graphite anode for an electrolytic cell for the electrolysis of alkyline salt solutions by the mercury process, the requirements for such graphite anode are that the graphite anode is resistant to nascent chlorine, has small overvoltage to chlorine, and is inexpensive, etc. However, the conventional graphic anode has the following defects. Namely, the graphite anode is not resistant to nascent oxygen and is porous, etc.

Hypochlorite ions, hydroxide ions and sulfate ions exist in an alkaliriesalt solution and these ions discharge, respectively, at'the anode to evolve oxygen gas, and a part of these ions react directly with the graphite anode to generate carbon dioxide, and further destroys the bonding which binds together the ne particles constituting the graphite anode and finally the anode is mechanically crushed.

Thus, as the graphite anode consumes, tine and coarse pieces of the crushed anode fall onto the surface of the cathode amalgam and decompose the sodium amalgam to give rise to an evolution of hydrogen.

If a further large amount of graphite pieces fall onto the surface of the amalgam, the pieces will be mixed with sodium amalgam to form a mercury paste of high viscosity, and the paste will adhere to the surface of the cathode iron plate and stay t-hereat with the result that not only lytic cell seriously interrupted but also the current eiliciency is markedly decreased, and if the concentration of sodium amalgam amounts to 1%, the cathode amalgam will lose entirely its uidityrand stick in a layer to the surface of the cathode iron plate to bring about an evolution of a large amount of hydrogen so that the electrolytic lcell can explode.

Since the degree of consumption of graphite anode as described above increases with the increase of current density and rise of temperature in the electrolytic cell, and the amount of chlorine gas evolved from the lower surface of the anode increases proportionally to the current density, the mechanical destruction of the graphite anode by chlorine increases so that it shortens'the life of the graphite anode and moreover the amount of fine particles of the crushed graphite anode is increased which fall onto the surface of the cathode amalgam.

On the other hand,since the anode graphite is porous, the electrolyte penetrates into the interior of the anode, and the supplying of chlorine ions is not suicient in the pores of the anode so that discharge of hydrogen and sulfate ions is brought about, oxygen is evolved, and as a result, the anode is swollen and subjected to oxidationconsumption, and thus, the anode is deteriorated.

Such a detrimental and harmful eifect is intensified with the rise of current density, the electric resistance of the graphite anode is increased, the electrolyzing voltage is increased, which results in a decrease of the original unit of electrolyzing power.

Reference is made to the anode pole to be connected to the graphite anode plate as follows:

There have hitherto been used many graphite poles, like a graphite anode plate, but this graphite is accompanied in this case by the following defects:

In the rst place, in the case where the current density has become high, the graphite pole never stands the load with its inherent resistance, and heat generation and voltage losses become larger. Secondly, the contact resistance at the connected portion of the anode pole and the anode plate is so large that operation under a high current density becomes impossible. Thirdly, the graphite pole becomes aged and consumed in the electrolyte solution and must be discarded within a few months. Fourthly, the connected part of the anode pole with the anode plate is also corroded by the' electrolyte solution and its electric resistance is increased in the course of its use. On account of the defects as described above, with regard to an anode pole adapted for operation under a high current density as much as about amp./dm.2, it is necessary to establish a process for using a metallic pole having lower electn'c resistance than graphite, as Well as for making an anode pole which can be completely connected to an anode plate where the said metallic pole is never corroded by salt water.

In order to accomplish the operation under an anode current density over 100 amp/dm?, the present invention teaches that it is essentially important in the first place n; that the anode has low electric resistance; in the second place, the anode is less consumed and has a protracted life and that in the third place the anode is not seriously aged over a long period of time.

In order to enable the invention to be more readily understood, reference is now made by way of example to the accompanying drawings which illustrate diagrammatically embodiments thereof, and in which:

FIG. 1 is a cross-sectional perspective view of an electrolytic cell for electrolyzing alkaline salt solutions by the mercury process, wherein graphite anodes produced according to this invention are set;

FIG. 2 is an enlarged view of a model, showing the internal structure of a conventional graphite anode;

FIG. 3 is an enlarged view of a model, showing the internal structure of a graphite anode according to this invention;

FIG. 4 is a perspective assembled view showing by way of example an embodiment of a graphite anode produced according to this invention;

FIG. 5 is a cross-sectional view taken on the line V-V in FIG. 4;

FIG. 6 is a perspective view showing by way of example another embodiment of a graphite anode produced according to this invention;

FIG. 7 is a cross-sectional view taken on the line VII-VII in FIG. 6;

FIG. 8 is a perspective view showing by way of example a further embodiment of a graphite anode produced according to this invention; and

FIG. 9 is a cross-sectional view taken on the line IX-IX in FIG. 8.

"Referring to the drawing in detail, wherein like reference characters indicate like parts throughout the several figures:

In FIG. 1, the electrolytic cell is composed of a cell body having connecting side walls 1 provided with rubber lining joined to a cathode bottom plate 3 through the medium of rubber packing 2. The anode according to this invention is composed of anode plate 5 an-d anode connector pole 4, and is immersed in an electrolyte solution 7 with which the electrolytic cell is filled. Said anode is suspended and set through openings 12a of a cover plate 12 on the electrolytic cell at the distance of a few millimeters from the surface of the cathode amalgam layer 6. FIGURES l an-d 2 show that the anode plate 5 is composed of graphite particles 8. As shown in FIG. 1, the anode pole 4 is directly coated with a protective layer 13 composed of chlorine-proof material, such as hard rubber, synthetic resin or the like, and completely protected on its lower part from the electrolyte solution 7 by means of a protecting ring 14 composed of chlorineproof material such as carbate, hard rubber, polyester resin, vinyl chloride resin and furan resin, carbon cement, powdered poreclain `and graphite.

FIG. 2 is an enlarged View of a model showing the internal texture of a hitherto known graphic anode, and as can be seen therefrom, the po-res of the graphite plate are lcompletely embedded and filled with synthetic resin, and consequently, when such a graphite is used in electrolysis the graphite readily cracks `due to the swelling of the resin.

FIG. 3 is an enlarged View of a model showing the texture of the anode plate according to the present invention, and the graphite particles 8 are bound or connected with each other by graphite tenacious bands 9. A film of synthetic resin latex is adhesively formed on the inner and outer walls of the boundary defined by the graphite particles 8 and tenacious bands 9, and spaces 10 are formed in the interior of the said boundary by evaporation of the said resin latex.

FIG. 4 is a perspective view showing one embodiment of the anode of the present invention, and in this figure the anode pole 4 having a protective layer 13 is connected to the anode plate produced by the specific treatment as described hereinafter through a protective ring 14 made of chlorine-proof material. Fu-rthermore with regard to this graphite anode pole, this anode connector pole can be substituted by a metallic anode pole made of metal, such as copper or brass, having lower electric resistance than that of the graphite. When such a metallic anode pole is employed, it is important to prevent the connected portion of the anode pole and the anode plate from the corrosion by the hot salt water containing chlorine.

FIG. 5 shows a sectional View taken on the line V-V of FIG. 4.

A tapered recess 16 is formed in the anode plate 5. The recess is then heated to about to 200 C. A layer 17 subjected to the chlorine-proof treatment is formed by penetrating chlorine-proof chemicals such as chloronaphthalene, chloro-parafiin, chlorinated fish oil and vegetable oil into the anode plate under pressure or at reduced pressure from the inner part of the said recess. The anode connector pole 4, which has been covered with the protective layer 13 completely to the position corresponding to the top end of the tapered portion 15, is fitted into the said recess by pressing. Thereafter, the protective ring 14 is adhesively secured around the said protective layer 13 on the said anode plate 1S with a chlorine-proof adhesive agent as a base and the chlorine-proof adhesive agent 18 is further applied on the connected part between the anode pole and the anode plate so as to completely prevent the intrusion of salt water.

FIG. 6 is a perspective view showing another embodiment of the present invention. The anode pole 4 having the protective layer 13 is directly and firmly tightened to the anode plate by means of a screw-threaded ring 19 adjacent the protective ring 14.

FIG. 7 shows the structure of the sectional view taken on the line VII-VII of FIG. 6. The anode pole 4 is fitted into the anode plate 5 by means of the tapered end in the same way as in FIG. 5, but in this case, a screwthreaded ring 19 is disposed underneath the protective ring 14, and the lower bottom part of the protective layer 13 is provided with a threaded screw 21, on which the screw-threaded ring 19 is screwed. It should be noted that the connection between the anode pole and the anode plate is more fortified by the above-mentioned construction and the connected part is perfectly prevented from errosion by salt water. Namely, the anode pole 4 is integrally formed with the screw-threaded ring 19, and the said screw-threaded ring 19 is set on the anode plate 5 by a chlorine-proof .adhesive agent 21. Since the protective ring 14 is further connected above the said screw-threaded ring 19 by means of chlorine-proof adhesive agent 18, the exfoliation of the anode pole 4 from the protective ring 14 by the thermal expansion due to the rise of temperatu-re is completely prevented.

FIG. 8 is a perspective view, showing a further embodiment 'of the present invention. The anode pole 4 having the protective layer 13 is bolted to the anode plate 5 with aid of a ring 23 and bolts 22.

FIG. 9 shows the structure of the sectional view taken on the line IX-IX in FIG. 8.

As shown in FIG. 9, the anode pole 4 is fitted into the anode plate 5 with aid of a tapered end in the same way as in FIG. 5, however, the lower part of the protective layer 13` is directly provided with a threaded screw 13a and not only the ring 23 having bolts is screwed on this part b-ut also bolt bores are formed in this ring `23, which is bolted on the anode plate 5 by means of bolts 22 made of chlorine-proof material. Between the ring 23 Ihaving bolts and the anode plate 5, the chlorine-proof adhesive 18 acts as a liquid packing. Accordingly, no exfoliation of the protective ring 23 from the anode plate 5 due to the thermal expansion of the anode pole 4 takes place and, moreover, since the anode pole 4 is secured to the anode plate 5y with aid of bolts 22, the supporting power by means of the anode pole 4 is much strengthened and the exfoliation of the protecting ring 23 from the anode plate 5 due to the strain on the anode pole 4 is completely prevented and no intrusion of salt water ta-kes place.

The anode plate produced by the specific treatment, which is the important point of this invention is further explained iny detail as follows:

Some representatives of conventional processes for penetrating the pores of a graphite anode carried out heretofore for the purpose of covering the porosity which is the defect of graphite anode, diminishing the consumption of anode and enhancing the original unit of graphite so as to accomplish the long-term continuous operation of the electrolytic cell are described as fol- Y lows:

Namely,

(1) Filling the pores of a graphite anode with parathn. v

(2) Filling the pores of a graphite anode with chlorinated oil. Y

(3) Filling the pores of a graphite anode with chloronaphthalene.

These known processes had great defects respectively and could only Ibring about some effect, and were successful'in the anode of the electrolytic cell used in the Ydiaphragm process, blut could not be applied to the mercury process.

The mechanism of each of the said processes is described in detail below.

In the first place, in the case where the graphite anode is filled with paraliin, as shown in FIG. 2, the pores 10a defined or surrounded by graphite particles 8 and graphite bands 9 in the graphite anode are iilled uniformly with paraffin. The consequence of the case where the anode is subjected to electrolysis in such -a state, is explained below:

First, the temperature in electrolyte solution reaches as high as 80 to 90 C. inthe case where the operation at high current density is popular these days. 'Accordingly, the paraliin in the inner part ofthe anode begins to melt and exudes in the bottom surface of the anode ,and simultaneously is converted into paratiin chloride by nascent chlorine, and thus, hydrochloric gas'is generated with expansion of the volume so that the graphite is destroyed and concurrently therewith the said chloride itself falls on thesurface of the cathode mercury and brings on the cause of an evolution of hydrogen.

`In the second place, in case where the graphite'anode is filled with chlorinated lish loil or chlorinated vegetable oil there takes place results similar to those in the case of paraffin, and the prevention of graphite integration due to the formation .of protective film on the surface of the gradually chlorinated anode, which is the proper object, cannot be achieved.

Furthermore, inthe case 'where the .anode is filled withchloro-naphtha-lene, the exudation and chlorination of chloro-naphthalene is rather slow, but the following defects are caused:

That is, as shown in FIG. 2, since the pores are spaces 10a in the anode are completely embedded wth chloronaphthalene, the swelling thereof ,gives -rise to cracks and crevices in` thegraphite' texture, and the eXfoliation occurs on the surface of .the anode and large graphite particles fall. And in thiscase, Vsince the chloro-naphthalene has no veffect to adhere ltoethe `surfaces of graphite particles and to include andv bind the whole, the chloro-naphthalenepromotes the-'further result in that the -chloronaphthalene exfoliates vas a mixture with lgraphite pieces and falls from the anode onto the surface of mercury, and the evolution of hydrogen gas becomes violent.

Moreover,'a carbateA product is `available on the market as graphite treated with synthetic resin but judging from the structure of the carbate product, extremely porous graphite is selected as a raw material and the. pores thereof are perfectly lled vwithl synthetic resin to make the graphite into a concrete structure, and therefore it is the main object of the said canbate product to impart the resistance against chemicals to graphite as well as to prevent it from the leakage of chemicals. Accordingly, the heat conductivity .and the anti-leakage properties of the product are excellent, but since the pores are completely filled with synthetic resin, in using this product in electrolysis the graphite cracks due to the swelling of synthetic resin embedded in the porous graphite and causes large particles which fall onto the surface of mercury to give rise to an evolution of hydrogen gas.

' This invention completely overcomes all the defects of the conventional processes and creates the following process for preventing the anode from consumption:

Namely, the graphite anode having the structure as shown in FIG. 3 was obtained by using synthetic resin latex. Tenacious films 11 of synthetic resin having a thickness of l to 10u are formed adhesivel-y on the inner and outer walls of anode pores while including and firmly binding the inner and outer surfaces of the graphite particles 8 and the tenacious jbands 9, and thereby the swelling and disintegration of graphite is prevented. Moreover, since the spaces 10 formed by evaporation of the water content in the resin latex do not cause cracks in the graphite by the swelling of the film of synthetic resin, and on account of electric non-conductivity of the film of synthetic resin a discharge of chlorine ions, hypochlorite ions and sulfate ions is prevented, and not only are the pores in the graphite free from disintegration but also the film can be formed by the least required amount of synthetic resin, `and as the result the amount of synthetic resin to be used is considerably less as compared with that in conventional processes and the treatment of the anode becomes very economical and inexpensive.

Moreover, as regards the synthetic resin latex used in this invention, the said synthetic resin latex can be uniformly and completely applied to the inner and outer Walls of pores in the anode graphite by a specific compounding, andthis brings about a favorable result in that no formation of large graphite particles by exfoliatiou "of the surface of -the anode can take place over a long- 'term use of the anode, and the stabilization of the inter- 'pole adjustment of the anode and the rationalization of the feeding of electrical current to the anode as well as Y the enhancing of the electrolyzing voltage are achieved.

The synthetic resin latex used in this invention for the above-mentioned purpose has the following characteristics. f Namely, this resin latex is chlorine-proof and heatresisting, has the property of forming a lilm Vat to 90 C., does'not decomposev at 80 to 90 C. and has an excellent property for penetrating into the graphite anode pores.

Examples of the synthetic resin latex are exemplified as follows:

. Copolymer or single polymer of vinylidene chloride, vinyl chloride, acrylonitrile and the like.

Furthermore, in order to improve the penetration of the resin latex, surface-active agents such as amionic soap, non-ionic soapand others may be added.

The'resin concentrationof the latex is preferably in the -rangeofv 5 to' 50%, depending on the kind of graphite anode used and the `conditions of use.y The processy of causing synthetic resin to adhere to inner or outerwalls 'of pores in graphite is described below:

Firstly, the anode isplaced in a vacuum vessel and the -air -in the anode is evacuated, and then synthetic resin latex is pouredinto the vacuum vessel, and thereafter the interior of Vthe vacuum vessel pressurized with the result that the tenacious resin latex filml is caused to -be adhesively formed on the inner and outer walls 4of pores, and'binds thegraphite particles and the tenacious bands.

With respect to the drying of the graphite anode after the latex coating, the temperature and the time of drying depend on the kind and the recipe of the synthetic resin, and the perfect adherence of the fil-rn of synthetic resin latex can be accomplished by drying at 50 to 100 C. for 4 to 10 hours.

Functions and eiects of the anode treated by the process of this invention are described as follows:

In the iirst place, the film of synthetic resin latex formed in pores in the anode plate is excellent in chlorineproof property and heat-resistance and can sufficiently be resistant to the shocks made by the rapid evolution of chlorine and oxygen from the surface of the anode when operating at high current density in the electrolytic cell, to disintegration due to swelling and shrinking of the anode caused by rapid change of temperature, and to mechanical abrasion due to the friction of chlorine gas on the surface of the anode.

In the second place, the anode of this invention is characterized in that the electric resistance of the whole anode is very low and the electrolyzing voltage when operating at high current density is extremely low.

y Namely, metal having small electric resistance is used as an anode connector pole, a tapered end is used in the connection thereof to the electrolytic plate and moreover, as the result of laborious studies on tapering angle and fitting pressure, the Contact resistance between the anode connector pole and the anode plate has been reduced to about one-fourth of that of a graphite pole so that no heat generation at the connected portion takes place even at a high current density about 100 amp/dm?.

In the third place, in the structure of the connected portion between the anode connector pole and the anode plate, the tapered part is soaked with non-permeable and Chlorine-proof material over its area and whole body from the inner surface of the tapered recess, and since the anode is constructed in such a way that it is not only prevented from the corrosion but also from strain and stress caused by thermal expansion, the anode of this invention has the feature of being capable of maintaining the electrolyzing voltage favorably over a long time.

In the fourth place, since the metallic anode pole is directly protected by the protective layer and consequently, the anode pole is preserved, and even in a case where the anode plate is consumed and discarded, the regeneration of the anode pole is possible if the protecting layer on the anode pole is renewed, andtherefore about 0.5 kg./t. NaOH, calculated on the original unit of graphite, can be cut down, as compared with a graphite pole.

In the fifth place, the process for producing an anode according to this invention is characterized in that the process is rather simple as compared to its great effects, home-working is easy and the working cost is inexpensive.

The following is an example rof this invention which gives alpreferred form of forming the anode.

Example Instance of the process for causing the synthetic resin latex to adhere rmly to the inner and outer walls of the pores in the graphite anode.

(1) Recipes of the resin latex used.

Percent Vinylidene chloride monomer 70 Vinyl chloride monomer 30 Concentration of resin Anionicsoap ,(in a small but effective amount), added,

(2) Process of working.

The results of using the anode worked` by the process according to the present invention are shown as follows, as compared with the conventional anode:

Conventional Electrode of Articles anode the present invention Passing current Kil. Amp 80 Current density Amp/(imi. 122 122 Electrolyzing voltage (volt.) 5. 0-5. 1 4. 5-4. 6 Temp. in electrolytic cell C 80f85 80-85 Time of using the anode (days) 8 16 Concentration of amalgam Na,

pereent 0.6 0.3 Concentration of hydrogen in chlorine,

percent. 0. 1-0. 5 0-0. 1 Current eciency, percent 97 Interval of cleaning electrolytic cell (months) 3-4 6-7 Initial unit of graphite Kg./t. NaOH 3. 5-4. 0 2. 0-2. 5

What is claimed is:

1. In a process for producing a graphite anode in an electrolytic cell having a mercury electrode 'for the electrolysis of alkaline salt solutions the steps comprising in combination, respectively,

(a) `forming a tapered recess in said graphite anode,

(b) heating the recess to about C. to 200 C.

(c) under pressure depositing a chlorine resistant material in the recess, said material being selected from the group consisting of chloro-naphthalene, chloroparafiin, chlorinated fish oil, chlorinated vegetable oil and mixtures thereof,

(d) maintaining the said material and recess under pressure for about 30l to 60 minutes whereby the material .penetrates into the graphite anode,

(e) forcing a conductive connector pole composed of a metal having a lower electrical resistance than graphite and having a tapered end into the recess with the tapered end fitting into the tapered recess in the graphite anode, any exposed .part of the pole being coated with chlorine resistant material, and

(f) applying a chlorine resistant sealing protective ring composed of a material selected from t-he class consisting of impervious carbon, graphite, hand gum, polyester resin and vinyl chloride, and adhesive around the connector lpole at the intersection of the pole and graphite anode to form a graphite anode with a firmly bonded connector pole.

2. A process as in claim 1 wherein any exposed area of the connector pole is coated with at least one chlorine resistant compound selected lfrom the group consisting of graphite, porcelain, carbon cement, furan resin, vinyl chloride resin, polyester resin and hard gum.

3. A process as in .claim 1 wherein in step (f) at least one screw threaded protective ring consisting of chlorine resistant material is lpositioned under the said sealing protective ring to firmly hold the said pole in position.

References Cited OTHER REFERENCES p Anc. Application of ou, ser. No. 326,756. Pribnshed May 1943.

JOHN H. MACK, Primary Examiner.

D R. JORDAN, Assistant Examiner. 

1. IN A PROCESS FOR PRODUCING A GRAPHITE ANODE IN AN ELECTROLYTIC CELL HAVING A MERCURY ELECTRODE FOR THE ELECTROLYSIS OF ALKALINE SALT SOLUTIONS THE STEPS COMPRISING IN COMBINATION, RESPECTIVELY, (A) FORMING A TAPERED RECESS IN SAID GRAPHITE ANODE, (B) HEATING THE RECESS TO ABOUT 150*C. TO 200*C. (C) UNDER PRESSURE DEPOSITION A CHLORINE RESISTAN MATERIAL IN THE RECESS, SAID MATERIAL BEING SELECTED FROM THE GROUP CONSISTING OF CHLORO-NAPHTHALENE, CHLOROPARAFFIN, CHLORINATED FISH OIL, CHLORINATED VEGETABLE OIL AND MISTURES THEREOF, (D) MAINTAINING THE SAID MATERIAL AND RECESS UNDER PRESSURE FOR ABOUT 30 TO 60 MINUTES WHEREBY THE MATERIAL PENETRATES INTO THE GRAPHITE ANODE, (E) FORCING A CONDUCTIVE CONNECTOR POLE COMPOSED OF A METAL HAVING A LOWER ELECTRICAL RESISTANCE THAN GRAPHITE AND HAVING A TAPERED END INTO THE RECESS WITH THE TAPERED END FITTING INTO THETAPERED RECESS IN THE GRAPHITE ANODE, ANY EXPOSED PART OF THE POLE BEING COATED WITH CHLORINE RESISTANT MATERIAL, AND (F) APPLYING A CHLORINE RESISTANT SEALING PROTECTIVE RING COMPOSED OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF IMPERVIOUS CARBON, GRAPHITE, HARD GUM, POLYESTER RESIN AND VINYL CHLORIDE, AND ADHESIVE AROUND THE CONNECTOR POLE AT THE INTERSECTION OF THE POLE AND GRAPHITE ANODE TO FORM A GRAPHITE ANODE WITH A FIRMLY BONDED CONNECTOR POLE. 